1. Field of the Invention
The present invention relates to a silicon nitride composition and a sintered product of silicon nitride having improved wear resistance and chipping resistance. The present invention also relates to articles of manufacture such as, but not limited to, a cutting tool and also to a cutting method.
2. Description of the Related Art
Silicon nitride and SIALON known as engineering ceramics have high heat resistance, thermal shock resistance, and oxidation resistance as well as high strength, high strength at high temperatures, and high toughness. Thus, progress has been made in the application of silicon nitride and SIALON to hot engine components, such as automobile engine parts, gas turbines and turbocharger rotors, and cutting tools. See, for example, U.S. Pat. Nos. 4,295,791 and 4,323,394, hereby incorporated by reference.
For example, sintered products of silicon nitride containing yttrium as a rare-earth element distributed in grain boundaries between silicon nitride grains are used for such purposes.
In cutting tools among such components, a force of a strong impact may be applied thereto. Thus, materials having improved impact resistance and chipping resistance have been required.
Although attempts have been made to improve mechanical and thermal properties of a sintered product of silicon nitride, still more improvement is necessary.
For example, proposed are a sintered product of silicon nitride including an amorphous grain-boundary phase containing a rare-earth element, silicon, aluminum, and traces of magnesium, which are used as metal components, and oxygen and nitrogen. These components in the grain boundary phase are controlled to a specific composition range.